An emulsion consists of two immiscible liquids mixed together with small droplets of one liquid dispersed in the other liquid. The dispersion is usually not stable and all the droplets “clump” together over time to form two layers or phases. An emulsifier is a substance that can stabilize an emulsion by increasing its kinetic stability, for example, by inhibiting droplet coalescence (i.e., preventing the droplets from clumping together). The majority of emulsions can be classified according to the chemical nature of the liquids, such as oil-in-water (O/W) or water-in-oil (W/O).
W/O emulsions are desirable in many industries (e.g., the cosmetics industry), yet many more emulsifiers exist that can stabilize O/W emulsions than W/O emulsions. Producing a stable W/O emulsion represents a challenge and only a few emulsifiers currently exist that can, by themselves (i.e., acting as a primary emulsifier), adequately stabilize such an emulsion. Furthermore, W/O emulsions comprising polar oils are particularly difficult to stabilize due to their amphiphilic nature. Thus, relatively few emulsifiers that can stabilize W/O systems have been described.
Esters can be synthesized from compounds such as vegetables fatty acids, fatty alcohols, and polyalcohols. The use of saturated fatty acids in esterification reactions can be advantageous, since they can produce stable and homogeneous esters (e.g., in the form of high melting point waxes or limpid liquids), without the formation of a liquid/solid heterogeneous phase. However, the use of unsaturated fatty acids in uncontrolled esterification reactions can lead to the formation of non-homogeneous products such as the formation of precipitates and the simultaneous presence of liquid and solid phases, which are often not desirable (e.g., for cosmetic emulsions).
Such problems are often caused by the presence of molecules having very different melting points. For example, saturated fatty acids (e.g., C18 fatty acids) exist as solids at room temperature, while unsaturated fatty acids (e.g., C18:1 fatty acids) exist as liquids at room temperature. Using non-homogeneous emulsifying compositions may lead to undesirable effects such as formulation instability, reduction of sensorial properties, and lack of efficacy. When dealing with such products with very different melting points, it can become necessary to use warm rooms or mechanical mixing procedures to homogenize the products before they can be used.
In some cases, the melting point of a raw material can be an important factor to consider. Solid compositions (e.g., waxes) require heat to be melted before they can be homogenized or emulsified with other ingredients. The use of elevated temperatures during processes/formulations required to pre-melt raw materials not only increases energy consumption (and thus manufacturing costs), but can also be problematic when working with thermolabile active ingredients.
Accordingly, there exists a need for novel emulsifiers, including emulsifiers capable of adequately stabilizing W/O emulsions that address at least some of the above mentioned problems.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.